The present invention is directed to a checkweigher for weighing objects moving along a conveyor. More particularly, the present invention is directed to a checkweigher with multiple scales and corresponding conveyor mechanisms for permitting the weighing of objects of different size/weight on a single checkweigher.
A checkweigher may generally be described as a high speed weighing device for the in-motion weighing of objects as the objects travel along a conveyor. A checkweigher is typically installed to a conveyor line such that an in-feed conveyor is provided for delivering objects to the checkweigher and a discharge conveyor is provided to transport objects from the checkweigher to a downstream location. The checkweigher itself also typically employs a conveyor to transport objects one at a time across a scale (weigh pan), which is essentially a vertically deflectable mechanism operable to effect weighing of the moving objects. The use of weigh pans in checkweigher would be well known to one of skill in the art and need not be described in detail herein.
The use of checkweigher to weigh moving objects is well known, and various checkweigher designs exist for this purpose. Nonetheless, checkweigher improvements have been proposed and put into operation over the years. One such improvement is described in U.S. Pat. No. 5,434,366 to Troisi, which is hereby incorporated by reference herein. This patent teaches arranging conveyor chains of a checkweigher to underengage an object to be weighed only immediately adjacent the periphery thereof. Arranging the conveyor chains in this manner minimizes the effective length of each product as seen by the checkweigher weigh pan, which permits a reduction in the length of the weigh pan and an increase in the stability of objects transported over the weigh pan. Such a design provides for a substantial increase in available settle time, as well as a reduction in conveyor speed in comparison to previously known checkweigher. In a preferred form of the invention, the length of the weigh pan employed may be reduced to be essentially equal to, and preferably equal to, the diameter of the objects to be weighed, thereby ensuring that only one container can be supported by the weigh pan during a weighing operation.
It is often desirable to convey objects of different size (e.g., diameter) over a single checkweigher. In certain checkweigher, this means providing a set of fixed width conveying elements (e.g., conveyor chains and tracks) that can support objects of different diameter. According to the improved checkweigher of U.S. Pat. No. 5,434,366, the conveyor chains are moveable such that their centerlines may be relocated to approximately the peripheral edges of a particular object to be weighed. Additional tracks are also provided to support the conveyor chains at the various positions necessary to support objects of various diameter. This allows for the above-described advantages even with objects of different size.
While a checkweigher of U.S. Pat. No. 5,434,366 provides for improved results when weighing objects of different diameter, weighing such dissimilar objects on any known checkweigher is still problematic. Particularly, it is an understood principal of checkweigher design that the best possible accuracy is achieved by using conveyor chains of the lightest possible weight. This stems from the fact that lighter weigh chain typically has a smaller pitch, which creates less noise as it travels across the weigh pan and, therefore, has less of an effect on weighing accuracy.
It is also understood that checkweigher conveyor chain size must be relatively matched to the size of the objects that will be transported thereon. That is, heavy objects require heavier chain. Past experience shows that attempting to run heavier objects on lightweight chain to improve weighing accuracy causes unacceptable, premature chain and runner (track) wear, even if the number of conveyor chains is increased (e.g., 4 chains are used instead of 2). Consequently, the use of multiple checkweighers is the solution typically employed when it is required to weigh both large and small objects on a single conveyor line. For example, two checkweighers may be associated with the same conveyor line: one checkweigher provided with lightweight chains for processing the smaller objects, and the other checkweigher provided with heavier weight chains for processing the larger objects. Objects to be weighed are then diverted to the appropriate checkweigher as they are conveyed. Unfortunately, this solution is not always feasible due to space constraints associated with a given conveyor line. Further, purchasing and installing two separate checkweighers can be quite expensive.